fossil

Fossil Coral (Rugose/Favosites)

Anthozoa (Rugosa or Tabulata)

Hardness: 3-4 (Calcite replacement) or 7 (Silica replacement); Color: Tan, beige, or gray; Luster: Dull to earthy; Structure: Radiating septa and honeycomb-like pores visible on the surface.

Hardness: 3-4 (Calcite replacement) or 7 (Silica replacement)
Color: Tan, beige, or gray
Luster: Dull to earthy

Identified July 18, 2026More fossil →

Explore Fossil Coral (Rugose/Favosites) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3-4 (Calcite replacement) or 7 (Silica replacement); Color: Tan, beige, or gray; Luster: Dull to earthy; Structure: Radiating septa and honeycomb-like pores visible on the surface.

Formation & geological history

Formed through the permineralization of ancient marine coral colonies, typically dating from the Ordovician to the Permian periods (approx. 488 to 251 million years ago) in shallow tropical seas.

Uses & applications

Primarily used as educational specimens, collectibles, and occasionally polished for lapidary work or jewelry (like Petoskey stones).

Geological facts

Many fossil corals are found in the interior of North America, indicating that areas like the Midwest were once covered by warm, shallow oceans. Rugose corals are also known as 'horn corals'.

Field identification & locations

Identified by the distinct geometric or radiating patterns that resemble modern coral structures. Common in limestone outcrops or as weathered pebbles in riverbeds across the Great Lakes region and Kentucky.

Other fossil specimens

See all

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary

Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

sedimentary

Fossiliferous Limestone

Biogenic Limestone with Brachiopod/Crinoid fragments

sedimentary

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil